A universal quantum key distribution method

Combining heralded pair coherent state （HPCS） with passive decoy-state idea, a new method is presented for quantum key distribution （QKD）. The weak coherent source （WCS） and heralded single photon source （HSPS） are the most common photon sources for state-of-the-art QKD. However, there is a prominent crossover between the maximum secure distance and the secure key generation rate if these two sources are applied in a practical decoy-state QKD. The method in this paper does not prepare decoy states actively. Therefore, it uses the same experimental setup as the conventional protocol, and there is no need for a hardware change, so its implementation is very easy. Furthermore, the method can obtain a longer secure transmission distance, and its key generation rate is higher than that of the passive decoy-state method with WCS or HSPS in the whole secure transmission distance. Thus, the limitation of the mentioned photo sources for QKD is broken through. So the method is universal in performance and implementation.